In most cases, oils and fats are present
as emulsions, such as water-in-oil (W/O) emulsion (e.g. margarine and butter)
or oil-in-water (O/W) emulsion (e.g. beverages, milk, and fresh cream). Some studies
have shown that oxidative deterioration of foods containing oils and fats may
be affected by light, temperature, metals, or peroxide contained in food. In
fact, oxidative deterioration is a large economic concern in the food and preventing
the oxidation of emulsion is of vital importance for the food industry.
In this study, the
effect of different concentrations of Tween 20 (0.5, 2.5, 5.0, 10 w% vs. oil)
on the oxidation of canola oil O/W emulsion was investigated. Oxidation was
conducted at 34°C in the dark and accelerated using 2,2-azobis
(2,4-dimethylvaleronitrile) (AMVN) and 2,2’-azobis (2-methylpropionamidine)
dihydrochloride (AAPH) as radical generators. Peroxide value (PV, mEq/kg) was
monitored as generation of the primary oxidation compound. Tocopherol content of oil was analyzed by high performance liquid
chromatography (HPLC). Particle size of emulsion was measured using an inverted
optical microscope (200x), and calculated with “Image J” software (National
Institute of Mental Health, Bethesda, MA).
The results showed that
PV was suppressed by Tween 20 in a dose-dependent manner in both emulsion
system using AMVN and AAPH, and the tendency of suppression was clearer in the
system using AMVN than in that using AAPH. Contrarily, there were no
significant differences in PV when emulsions were prepared with
tocopherol-stripped oil. The particle size of emulsion droplets were also
consistent among emulsions prepared. However, tocopherol contents at lipid
phase of the emulsions prior to oxidation decreased with concentration of Tween
20.
In conclusion, although
the effect was modest, excess amount of Tween 20 modified the antioxidant
efficacy of tocopherol in a dose-dependent manner. The speculation is that
Tween 20 can help tocopherol to migrate from the lipid phase to the oil-water
interphase, where the oxidation occurs. Further research to define the optimum
combination of oil, water, and emulsifier is required.
Article by Yukihiro
Yamamoto and Rino Misawa, from Prefectural University of Hiroshima, Shobara,
Japan.
Full access: http://mrw.so/517D53
Image by Indirect
Heat, from Flickr-cc.
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